Mass spectrometers and other systems are used for measurement of the concentration of analytes or the detection and measurement of contaminants and trace additives in solutions and gases. As one example in the field of semiconductor processing, process solutions for wafer cleaning, etching and other forms of surface preparation are routinely analyzed using mass spectrometers with plasma ionization sources, one type is an inductively coupled plasma mass spectrometer (ICP-MS). The measurements made by ICP-MS are used to determine and manage the quality of process solutions. Ultrapure water (UPW), dilute hydrofluoric acid (HF), and standard industry clean formulations SC1 (Standard Clean 1, ammonium hydroxide and hydrogen peroxide in water) and SC2 (hydrochloric acid and hydrogen peroxide in water) are examples of solutions that are routinely analyzed. Quick and accurate analysis in these and other industrial process solutions can result in the early detection of contamination problems, better control of process chemistry, and ultimately lead to higher yields and less product variation. It is noted that the application of the method and apparatus described herein is not limited to industrial process control solutions but is applicable to use in life sciences, environmental and other applications as well.
Mass spectrometry is often the technique of choice to achieve sensitivity for trace and ultra-trace analysis in which the analyte concentration may be as small as parts per billion (ppb) or sub-ppb such as parts per trillion (ppt). For example, commonly assigned U.S. patent application Ser. Nos. 10/086,025, now U.S. Pat. No. 7,220,383, and 10/094,394 disclose automated analytical apparatuses that measure contaminants or constituents present in trace concentrations, the full disclosures of which are hereby incorporated by reference for all purposes. As disclosed in these applications, a sample is extracted having an analyte to be characterized. The extracted sample is spiked with a spike related to the analyte. For example, the spike may be an isotopically-altered version of the analyte as practiced in isotope dilution analysis or the spike may be a chemical homologue of the analyte as practiced in an internal standard analysis. The sample/spike mixture is then ionized and its mass spectrum determined in a mass spectrometer. The responses of the analyte and the spike in the mass spectrum enable a ratio measurement to be performed to, for example, characterize a concentration of the analyte in the extracted sample.
In another example, commonly-assigned U.S. patent application Ser. No. 10/004,627, now U.S. Pat. No. 6,974,951, which is incorporated by reference in its entirety, discloses an automated analytical apparatus for measuring contaminants or constituents present in trace concentrations using In Process Mass Spectrometry (IPMS) and an electrospray ionization source. In the IPMS technique, a sample of interest is spiked with a known amount of an appropriate isotopically enriched species and/or natural abundant species. This spike is to be used as an internal standard during the mass spectrometry measurement. In this technique, the relative ratios of peak areas present in the mass spectra of the sample species of interest and the isotopically enriched species and/or natural abundant species are used to determine the concentration of the chemical constituents of interest in the sample.
Sensitivities for trace constituents including organic species, molecules and trace metals such as Cu, Cr, Zn, Ni, and Co down to a one part per trillion (ppt) and beyond are potentially possible. UPW, HF, SC1, SC2, and other semiconductor process chemistries can be analyzed. Constituent concentration or contamination levels can be quantified through IPMS or other suitable methods. In one embodiment, IPMS combines the sample with an isotopically enriched calibrated spike. The spike serves as the calibration reference for determining the analytes by comparing relative ratios.
Trace contaminant metrology (TCM) and chemical composition metrology (CCM) tools, both available from Metara Inc. of Sunnyvale, Calif., rely on an electrospray ionization time-of-flight mass spectrometer (ESI TOF MS) for the measurement and quantitation of analytes. With continued sampling and analysis, contaminants and residue (e.g., silica) from the samples and/or solutions used in the process (e.g., SC1) may accumulate in the sampling and analysis pathway, in particular reducing or blocking the flow through the electrospray probe and/or sampling tube, causing inaccuracy, lower resolution, and/or lower sensitivity for the measurements. In order to acquire high resolution data with high sensitivity, a clean and well-maintained mass spectrometer system is needed.
Furthermore, the performance and efficiency of electrospray and other ionization techniques are often affected by the surface condition of the ionization apparatus. Optimum and stable operation of the ion source requires that the surfaces of the ionization apparatus are “conditioned” to a state where they are in equilibrium with the process solution that is being analyzed. Reconditioning is the process by which this state is induced in the shortest possible time.
Accordingly, apparatus and methods for cleaning and reconditioning of inline and automated chemical analysis systems are highly desirable to improve accuracy, precision, and efficiency.